Shaft Such as a Camshaft for Internal Combustion Engines

ABSTRACT

A shaft, such as a camshaft for use in the internal combustion engine of a motor vehicle, in which the shaft includes a basic shaft body, a plurality of functional bodies, such as cams, mounted in axially spaced positions on the basic shaft body, and at least one balancing element mounted on the basic shaft body, in which the at least one balancing element is produced separately from the basic shaft body and from the functional bodies, and the functional bodies and the at least one balancing element are subsequently mounted on said basic shaft body, for example, by axial press fitting.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of international application no.PCT/DE2006/001379, filed Aug. 7, 2006 designating the United States ofAmerica, and published in German on Feb. 15, 2007 as WO 2007/016914, theentire disclosure of which is incorporated herein by reference. Priorityis claimed based on Federal Republic of Germany patent application no.DE 10 2005 036 994.4, filed Aug. 5, 2005.

BACKGROUND OF THE INVENTION

Camshafts are used to control the gas exchange valves in internalcombustion engines. In a four-cycle engine, the camshafts rotate at halfthe engine speed. The control elements used to move the gas exchangevalves are cams consisting of base circle areas and radially elevated orlobed areas. An end piece to receive the chain wheel or gear wheel or asensor wheel and other elements may be additionally provided, forexample, on the camshaft.

In accordance with their function the cams on the camshaft are mountedoffset in the longitudinal axis. As a result, the camshaft as a whole isimbalanced, which can lead to additional undesirable engine vibrationsat least in certain speed ranges.

Furthermore, all the rotating masses of the engine cause vibrations. Atleast some of these vibration phenomena can be compensated in practiceby installing counter-imbalances. These counter-imbalances can bebalancing weights on the camshaft, and/or so-called balancer shafts canbe provided specifically for this purpose.

Published German patent application nos. DE 40 30 568 C2 and DE 43 36809 C2 describe the use of balancing weights in camshafts. In oneembodiment of DE 40 30 568 C2, balancing masses are eccentrically offsetrelative to the axis of rotation to compensate imbalances in a solidcamshaft. In another embodiment, balancing masses in the form of tubularsections are likewise eccentrically offset relative to the axis ofrotation. Such shafts are expensive to manufacture and have limitedapplication.

DE 43 36 809 C2 proposes that cams mounted to the shaft be provided witha bore and mounted to a basic shaft body. On the side of the camopposite the cam lobe the cams have a balancing mass in the form of aprojection configured as an axial extension, namely a half shellintegrally formed with the cam. Such camshafts again have limitedapplication because the position of the cams and the balancing weightmust be defined in advance in relation to each other and cannot bevaried.

SUMMARY OF THE INVENTION

It is an object of this invention to provide particularly camshafts andmethods for their production, where production is simpler and morecost-effective and the balance/imbalance distribution can be carried outmore precisely than before.

Another object is to expand the possible applications and uses ofcamshafts and also to take into account the mass distribution of othercomponents that are mounted, or to be mounted, to the shaft.

These and other objects are achieved with a shaft, such as particularlyin the camshaft having functional bodies provided on the shaft body,such as cams, in that the balancing masses are elements producedseparately from both the functional elements, such as cams, and theshaft, and are mounted to the shaft, such as the camshaft, for example.These elements can be fixed either to the cam itself or to the basicshaft body.

A particularly advantageous manner of mounting these elements is axialpress fitting, so that these elements are axially and rotationally fixedon the shaft. It can be particularly advantageous if both the cam andthe compensation or balancing elements or weights are fixed by axialpress fitting. For example, the cam and compensating elements can beaffixed to the basic shaft body by sliding the elements into desiredpositions on a tubular shaft and then expanding the tubular shaft by ahigh hydraulic pressure in the interior of the tubular shaft to achievea rotationally secure connection between the cam and compensatingelements and the shaft as described in published German patentapplication no. DE 40 30 568. Alternatively the cam and compensatingelements can be affixed to the basic shaft body by sliding the elementsinto desired positions on a smooth tubular shaft and then shrink fittingthe elements onto seats formed on the shaft to form a secure connectionas described in published German patent application no. DE 43 36 809.Another possibility is to slide the cam and compensating elements onto atubular shaft with a reinforcing sleeve of greater diameter disposedbetween successive elements, the sleeve having collar regions of reduceddiameter extending underneath the cam and compensating elements and thenhydraulically expanding the tubular shaft and the sleeves to clamp thesleeves between the tubular shaft and the cam elements in a forcelocking way as described in U.S. Pat. No. 4,993,282 (=DE 38 03 683). Seealso U.S. Pat. No. 6,286,196 (=DE 198 31 333); U.S. Pat. No. 6,804,884(=DE 199 38 791), and US patent publication no. 2004/134063 (=DE 101 01539). The entire disclosures of all these documents are herebyincorporated herein by reference.

Balancing weights or elements that are mounted to a basic shaft body byaxial press fitting are preferably annular and have a balancing regionwith a larger mass and a support region with a smaller mass. Compared tothe balancing region having the larger mass, the support region can havea smaller axial extent than the balancing region. The support region canalso be asymmetrical to the balancing region in a plane perpendicular tothe axis of rotation.

The balancing elements can also be configured at least approximatelylike a half shell and mounted to the shaft body. They can be secured bylaser beam welding, as well as by soldering or bonding. It isparticularly advantageous to secure them using capacitor dischargewelding, because capacitor discharge welding causes no warping andpractically no heating of the area surrounding the weld. If welding isused to secure the elements, it may be advantageous if the balancingelements have at least one inwardly directed contour. This contour caneven take the form of a bead extending at least axially parallel, whichin the welding process produces the joint with the camshaft or the basiccamshaft body.

Balancing elements or balancing weights with different masses can bemounted to one and the same camshaft.

The functional separation of cam control and mass compensation usingseparately produced balancing elements or balancing masses also makespossible a modular construction of the camshaft. The same basic camshaftbody can be used with different cams and corresponding balancing massesdepending on the requirements and the application. It also offerssignificant tool cost savings.

The invention also makes it possible in a particularly simple andadvantageous manner to take into account the mass of the other elementsmounted, or to be mounted, to the shaft, such as a sensor, a drive wheelor the like, by means of the number and position of the centers ofgravity of the balancing elements.

It is further possible in a particularly advantageous manner to disposethe balancing weights or elements on the shaft in such a way that theshaft itself has an imbalance, which however compensates or equalizesvibrations produced by other rotating masses.

A further inventive concept relates to the production of so-calledjointed shafts with non-round functional bodies, i.e., camshafts, forexample, in which cams are mounted to a basic shaft body using axialpress fitting. It has been found that in this type of camshafts, inwhich the cams are first ground to the specified contour and then pressfit, the external form of the cams differs from the specified contour,so that engine control is negatively affected. Not only the cylindricalmounting region is deformed but there are also deformations in theradially elevated or lobed region of the cam. Therefore, the object ofthe further inventive concept was to prevent such deformations and, inparticular, to create camshafts in which the outer contour of thefunctional bodies, i.e., the cam, for example, also corresponds to thespecified contour in the mounted state. This is achieved by clamping thecam by its inner bore using a clamping element, such as a hydraulic ormechanical mandrel, as the outer contour is ground. This produces anexpansion of the cam, which corresponds to the expansion after mountingof the cam to the camshaft. This makes it possible to produce the outercontour exactly in accordance with the specified contour.

Another inventive concept relates to the configuration of functionalbodies, particularly cams for a jointed camshaft. The object of thispart of the invention was to save material, make camshafts cheaper andreduce the imbalance in camshafts. According to the invention this isachieved by forming a recess in the cam that axially penetrates the camin the cam lobe at least in part. This recess can be axially continuousor can optionally penetrate the cam only in part. The recess—as viewedin the direction of the front side of the cam—can be sickle shaped andcan be formed from only one side or from both sides. The recess,however, can also be a continuous, at least approximately circularopening.

It is clear that this saves a substantial amount of expensive material,which would otherwise be needed in solid cams.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described in further detail hereinafter withreference to illustrative preferred embodiments shown in theaccompanying drawing figures, in which:

FIG. 1 is a side elevation of an illustrative camshaft constructed inaccordance with the present invention.

FIG. 2 is sectional view taken along line II-II of FIG. 1 showing theconfiguration of a first balancing weight;

FIG. 3 is a sectional view taken along line III-III of FIG. 2;

FIG. 4 is a sectional view taken along line IV-IV of FIG. 1 showing theconfiguration of a second balancing element;

FIG. 5 is a sectional view taken along line V-V of FIG. 4;

FIG. 6 is a sectional view taken along line VI-VI of FIG. 1 showing theconfiguration of a third balancing element;

FIG. 7 is a sectional view taken along line VII-VII of FIG. 6;

FIG. 8 is a view of a weldable balancing weight;

FIG. 9 is a sectional view of another balancing weight embodiment; and

FIG. 10 is a sectional view taken along line X-X of FIG. 9.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

FIG. 1 shows a so-called jointed camshaft 1 with a basic shaft body 2,comprised of a tubular section 2 a and a partially hollow end piece 2 bfixed thereto, for example, by welding, friction welding or the like.The end piece 2 b can be produced by solid forming and is connected at 2c to pipe 2 a using the methods described above. The extension 2 b has aflange 3 on its side opposite the joint. After the pipe section 2 a andend piece 2 b have been joined, the surface of the shaft-like basic bodyis finish-machined from the end region 4 to the start of the collar 5and prepared for axial press fitting of cams N1 to N8 and the balancingweights. These are then axially press fit in the appropriate sequence ina manner described in the above-cited German laid-open applications. Thesensor wheel 10 can be similarly mounted. At its end 4 the hollow shaft2 a is terminated by a sealing cap 11 to prevent oil from penetrating itand producing an imbalance.

The balancing weight 6 is shown in FIG. 2 in a view in the direction ofarrows II-II of FIG. 1 and also in FIG. 3 in a section taken along lineIII-III of FIG. 2. It has a support portion 12 formed as a partialcylinder and an region 13 having a greater radial extent and therefore alarger mass.

The balancing element 7 shown in FIG. 4 in a view in the direction ofarrows IV-IV is asymmetrical in the plane perpendicular to the axis ofrotation—as illustrated in a section in FIG. 5 taken along line V-V ofFIG. 4. This balancing weight or balancing mass 7 also has a supportregion 14 configured as a partial cylinder and an region 15 having alarger mass. To shift the mass center of gravity X axially closer towardthe support region 14, region 15 having the larger mass is conical,i.e., its mass decreases in axial direction away from the annularsupport region. The conical configuration is identified by referencenumeral 16.

FIG. 6 shows the balancing element 9 in a view in the direction ofarrows VI-VI. FIG. 7 shows the balancing element 9 in a section takenalong line VII-VII of FIG. 6, again with a partially cylindrical supportregion 17 and an region 18 with a greater mass. Here—as in FIG. 5—theradial and axial extent of region 18 is again substantially greater thanthat of region 17.

Instead of mounting at least single balancing elements 6 to 9, it isalso possible to mount the balancing weights shown in FIG. 8 to thebasic shaft body. The balancing elements 30 are at least approximatelyhalf-shell-shaped and have a contour 31 in their radially inner areathat is adapted at least approximately to the basic shaft body. Two weldbeads 32 protrude radially inwardly from this contour, so that thebalancing elements 30 can be welded to the basic shaft body, using, forexample, capacitor discharge welding, resistance welding or the like,such that the two weld beads 32 melt onto the basic shaft body.

FIG. 9 shows a side view of the cam N2 of FIG. 1, and FIG. 10 shows asection taken along line X-X of FIG. 9. The cam 3 has a bore 60 and apartially cylindrical region 61 that merges into a radially elevated orlobed region 62. A recess 63 is formed in the lobed cam region 62 tosave material and weight. The recess 63 can also be axially continuous.

Such cams are produced by corresponding operations, i.e., forging,optionally abrasive blasting, turning of the bore 60, hard turning ofthe bore to the fitting dimensions, grinding the peripheral contour andoptionally final barrel polishing to the finishing dimensions. However,when the cams are axially press-fitted via their bore 60, the outer formof the cams changes relative to the specified contour, i.e., not only inthe cylindrical region 61 but also in the lobed region 62. To ensurethat the cam's shape corresponds exactly to the specified contour evenin the press-fitted cam, the cam 3 is held by a clamping device via itscircular inner bore 60 when the outer contour 64 is ground so as toexpand the cam in the same manner as in the axial press fittingoperation. To this end, the cam can be held on a mechanical or hydraulicclamping element to produce the same kind of overlap as in the cam thatis press-fitted onto the shaft. This makes it possible to finish theouter contour exactly to the specified contour. After the tension isreleased, the shape of the element is not as specified, but once the camis mounted it meets the specification again.

The foregoing description and examples have been set forth merely toillustrate the invention and are not intended to be limiting. Sincemodifications of the described embodiments incorporating the spirit andsubstance of the invention may occur to persons skilled in the art, theinvention should be construed broadly to include all variations withinthe scope of the appended claims and equivalents thereof.

1. A shaft comprising a basic shaft body, a plurality of functionalbodies mounted in axially spaced positions on said basic shaft body, andat least one balancing element mounted on said basic shaft body, whereinsaid at least one balancing element is produced separately from saidbasic shaft body and from said functional bodies and said functionalbodies and said at least one balancing element are subsequently mountedon said basic shaft body.
 2. A shaft as claimed in claim 1, wherein saidfunctional bodies comprise cams mounted in axially and rotationallyspaced positions on said shaft, and said shaft is a camshaft.
 3. A shaftas claimed in claim 2, wherein the cams and the at least one balancingelement are both axially and rotationally fixed to the basic shaft bodyby axial press fitting.
 4. A shaft as claimed in claim 3, wherein thebalancing elements are annular and comprise a balancing region with alarger mass and a support region with a smaller mass.
 5. A shaft asclaimed in claim 4, wherein the support region has a smaller axialextent than the region with the larger mass.
 6. A shaft as claimed inclaim 4, wherein the support region, in a plane perpendicular to theaxis of rotation, is asymmetrical relative to the region with the largermass.
 7. A shaft as claimed in claim 1, wherein the balancing elementsare at least approximately half-shell shaped and are mounted to theshaft body.
 8. A shaft as claimed in claim 7, wherein the balancingelements are welded to the shaft.
 9. A shaft as claimed in claim 7,wherein along their inner contour of the balancing elements, thebalancing elements have at least one inwardly directed contour.
 10. Ashaft as claimed in claim 9, wherein the contour is a bead extending atleast approximately parallel to the shaft axis.
 11. A shaft as claimedin claim 1, wherein the balancing elements are secured to the shaft bywelding.
 12. A shaft as claimed in claim 11, wherein the balancingelements are secured to the shaft by resistance welding.
 13. A shaft asclaimed in claim 11, wherein the balancing elements are secured to theshaft by capacitor discharge welding.
 14. A shaft as claimed in claim 1,wherein a plurality of balancing elements are mounted on one shaft, andsaid balancing elements have different masses.
 15. A shaft as claimed inclaim 1, wherein the balancing elements have centers of gravity whichare positioned to take into account the masses of other elementsmounted, or to be mounted, to the shaft.
 16. A shaft as claimed in claim1, wherein the balancing elements are provided on the shaft so that theshaft itself has an imbalance.
 17. A shaft as claimed in claim 1,wherein at least one cam has an axially extending recess in its lobedregion.
 18. A shaft as claimed in claim 17, wherein said recess isaxially continuous.
 19. A method for producing a non-circular functionalbody for press fitting onto a shaft, said method comprising; clampingthe functional body onto a mandrel whereby the functional body isdeformed into a state corresponding to deformations which arise when thefunctional body is press fit onto the shaft; grinding the functionalbody to a specified configuration; releasing the ground functional bodyfrom the mandrel, whereby the functional body departs from the specifiedconfiguration; and press fitting the functional body onto the shaft,whereby the functional body reassumes said specified configuration. 20.A method as claimed in claim 19, wherein said functional body is a camand said shaft is a camshaft.